64 Section 1 Introduction to Collision Repair
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arrangement. If we were to raise A and lower B, the
panel would return to its original shape.
Another example of lateral force is shown in
Figure 4-13. In this example, the low-crown panel
is held securely at points A and B so that the edges
cannot move. A force is applied at C. As demon-
strated in the previous example, metal is usually
drawn in by lateral force. In this example, however,
this cannot happen. Therefore, a buckle forms at C
and the grains from C to the attachments A and B
elongate, or stretch. The surface area of the metal
permanently increases. This type of damage is simply
called a dent. There is a limit of stretch, depending
on the plasticity of the sheet metal. Once the limit of
stretch has been exceeded, the metal will tear.
When lateral force acts on a high-crown area, the
result is different. Roll a sheet of copy paper into a
cylinder and tape the ends so it will not unroll. Push in
on the crowned surface. Look at the inside and outside
of the cylinder. The deformation that occurs is similar
to what happens when a high-crown panel is damaged
by a side (lateral) impact. The force moves through the
crown above and below the point of impact. Instead of
stretching as a low-crown panel would, the high-crown
panel collapses. As the force travels through the high
crown, buckles form. The buckles become work hard-
ened and resistant to force. The buckles indicate how
far the force traveled through the panel. This type of
damage is called an arrowhead. Arrowheads can also
be formed by longitudinal force acting on a high-crown
panel. Demonstrate this by pushing on one end of the
paper cylinder. The force should form an arrowhead in
the cylinder.
A B
B
A A
B
C
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Figure 4-11. Notice how the paper buckles at the fold.
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Figure 4-13. A—Grains in a low-crown panel.
B—When a lateral force is applied to a low-crown
panel, the grains elongate, resulting in stretch.
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Figure 4-12. The force at C causes points A and B to
move toward each other.
A
B
A B
C
A
B
Colllapsed-hiinge Co Co Co Co Co Co Co Co ll ll l ll ll ll ap ap ap ap ap ap ap aps ap a se se se e s s d- d- d- d- d- d- d- d d hi h hi hi hi hi hi hi i ng ng ng ng ng ng ng ng ng ng ng e e e e e e e e e
buckle bu bu bu bu bu u ck ck ck ck k ck k ck k c le le e le le e
panel is attached at points A and B. In this example, the
attachments allow some movement. When the force is
applied at C, the attachments at A and B begin to move
toward each other. If the force is removed before attach-
ments A and B begin to resist movement, there will be
no buckling at C. The “drawing in” of A and B will absorb
the force at C, so the force will not act on the grain